Tuesday, December 29, 2015

Comparing the 95 db and 70 db signals. What errors you can see are probably due to me being lazy and using the Logitech Squeezebox volume control.

Distortion elements

Please note that while the shape of the distortion in these charts is accurate the scale is NOT! You cannot read the actual distortion values off these charts due to a limitation (or feature) in OmniMic. The distortion figures on on a scale not shown. What I will say here is that the actual distortion figures are ridiculously low all the way to 100 db. :)

Saturday, December 12, 2015

A big thanks go out to Bill Waslow for his excellent and free XSim. Together with OminMic and DATS I did in weeks what it would have taken me years if ever.

To make the long story short, here is a comparison between the simulated crossover, and XSim's expectation. Blue is simulated. Differences in phase are probably due to inexact placement of the microphone between early measurements and now.

Saturday, December 5, 2015

Sorry about the part numbers. I can't reorder them. On top is the 2nd order design, on the bottom is the first order.

Here we have the impedance of each, seen from the amplifier's point of view:

The top, yellow curve is the 2nd order filter, the bottom green line is the first order.

Next, let's take a look at the power dissipation in the series resistors in each.

R1 and R6 are part of the first order , R3 and R5 part of the second order filter. You can see in each case the power of the 2nd order filter lags (is lower) than the first order filter, except at the very end for the first resistors in the circuits.

Here are the simulated frequency responses, but please bear in mind having a good response was not part of the experiment. Tweaking the crossover becomes very arbitrary. The goal of this experiment was just to examine how power and impedances changed based on 1st vs. 2nd order. Also, the first resistor is not really needed, it's again there for the investigation.

Friday, November 27, 2015

What do you do when you have a long weekend, great new speaker drivers and your crossover parts are still a week away? Improvise!

The Noes design calls for a 2.8kHz crossover point with a 3-5 db tweeter pad, among other things. My plan was to tinker with the crossover during the long Thanksgiving weekend, and have them close to finished by Monday. So I had two choices:

Do nothing and use the woofer full range

Find crossover settings that would work with the parts I had.

Desperate, I chose the latter. I ended up with a crossover point at around 6.8kHz with the tweeter about 5 db lower than desired. Why? I only had 10 ohm power resistors left in my arsenal, and this was the lowest I could cross the woofer over with the parts I had.

How does it sound and look? Surprisingly good!

Thanks to Omnimic I was able to quickly tell I had to reverse the tweeter. Not my favorite situation, but desperate times call for desperate measures!

I've had the opportunity to listen to some fabulous recordings via our local classical internet station, KDFC. The Mundorf AMT's are spectacular, I can't wait to finish the real crossovers.

The crossover breadboards. The top section is the tweeter, bottom is the woofer.

Tuesday, November 24, 2015

I still don't have crossover parts, but that's no reason why I can't do some interesting measurements.

Fee Air ScanSpeak Impedance

Fresh out of the box in free air the speaker resonance is around 49 Hz at around 31 Ohms. I believe I read somewhere that ScanSpeak specifies the Fs after break in, so I should probably measure this again in a week or so.

To begin with, a full-range frequency response chart for the woofer. Incredibly clean at the upper end of the spectrum, even when averaged at 1/24th octaves. This is with the speaker on a chair and microphone 3ft away on the woofer axis.

Next up is the impedance measurement in the cabinet. The woofers have only been playing for about 4 days with low to medium jaz 24 hours a day. I'm going to have to go back to Lee to ask for help interpreting both of these. From the first chart I worry the box is a little large. Below is the chart I really don't know well, the speaker + cabinet impedance.

I can see the port resonance at 24 Hz, and a second resonance at 69 Hz. The valley's nadir is around 35 Hz, somewhat lower than the driver's Fs when first purchased. ScanSpeak specifies the Fs at 33 Hz after break in, in which case the tuning would be spot on.

I have a week before I can assemble the crossover, so I have time to plan ahead. With Thanksgiving coming up parts will be slow in arriving.

Saturday, November 21, 2015

Well, at least the first speakers I have designed from the ground up, and I use the term "design" loosely. Component selection was mine, cabinets are from Lee Taylor of Taylor Speakers, partial crossover design was from Madisound. I say partial because they designed a crossover for a different tweeter than you see here.

The cabinet is much better looking than this, especially the veneer. I'm afraid my phone doesn't do the quality of Lee's work justice, so please bear that in mind. His web site has pictures much closer to reality.

In a sense, this is a fail. I was trying to design some smaller satellites with these components, and Lee was trying to guide me to a floor stander. These speakers are really very tall and deep so I'm not sure most satellite stands would work for them. It's a bit like trying to have a baby and getting twins though, I am not at all unhappy! I just got more than I was expecting.

Drivers

The original design called for a smaller Mundorf AMT tweeter but that was out of stock and weeks away from arriving in the U.S. so i went for it's bigger brother the Mundorf AMT 25CM1.1-R. One weird thing about this driver is that it takes banana plugs, not spades or bare wires.

Thd mid-woofer remains the same though, the ScanSpeak Revelator 18W/4531-G00 7" driver. The 4 Ohm version is more sensitive so mean less damping is needed in the tweeter section. I chose the Revelator in part out of cost ($220 vs. $320 ea.) concerns but part was also that in the high end of the driver I liked the response better than it's Illuminator counterpart, then when I read that Zaph rated the Revelator better than the Illuminator in terms of distortion that cinched it for this design. I admit the basket does not look as cool though.

Despite the larger tweeter having a lower useful crossover point I'm keeping the crossover frequency the same for a number of reasons.

I don't want to redesign the crossover from scratch

Higher crossover frequency = higher power handling

One big advantage here as well is controlling the vertical dispersion. The taller the tweeter, the less floor and ceiling reflections and clearer the sound at the listening position. Like ribbons and electrostatic speakers, we should get enhanced clarity and detail than with conventional round drivers.

Test Wiring

Per Lee's suggestion I'm going to keep the crossover external until I have tweaked it perfectly. For this to work of course I'll use a separate pair of banana jacks for each driver. Internally I'm using plain old 14 gauge zip cord which happens to be made by Monster. I had it lying around from the surround sound installations in previous apartments. It's thick, flexible, finely stranded and best of all, free and taking up space under my bed in the wiring box.

The white cable with the bananas of course goes to the tweeter, the pinkish cable to the SS woofer. This being a test harness I didn't want to spend too much effort, but after installation and looking at the kinks in the wires I decided that the heat shrink was going to be necessary for proper strain relief.

The Sound!

Of course, anyone with a checkbook and drill can get speakers this good looking, but how do they sound? Magnificently quiet. You've never heard speakers that disappear like these..... My secret? They don't work yet! :( Crossover parts were delayed due to a series of errors on my part but I should be able to start putting that part together soon. Of course, being unable to resist, I am currently breaking them in by running the woofer's full-range. They sound surprisingly good by themselves! I had to go back to the charts and look but they have useful output to 10 kHz so I can run these as my main speakers without going completely nuts due to the lack of treble.

Sunday, November 15, 2015

I'll be posting more info on this in the DIYaudio forums, but for now here are the pics.

The chart below shows the final measurements, taken from my seating position with 1/24 octave smoothing and a 2mSecond window. The RED trace is with the grill (as recommended) and the BLUE trace is with the grill removed:

The image below is from the Sound and Vision review with the grill on. Note in particular the 10K peak and ragedness around 5kHz which are gone, those are probably thanks to the liberal use of felt on the grill and tweeter housing:

And lastly the grill removed, which is the image most make fun of:

Not only is the grill less important, but the tweeter balance is different. Instead of trying to push the tweeter up at the last octave, I've gone for a smoother response from 2-10k, that goes generally downward. Crazy? Well, by accident it actually measured much closer to the Focal Utopia's of 2004. Check out this chart from Stereophile:

Of course, I'll never get the output, especially in the bass, of the Utopia, but it does sound much smoother and coherent than it did before. Should you buy a Profile 918 and hack the crossover like I did to get a poor man's Utopai? No way. The value just isn't there overall. The value IS there if you want to take this on as a learning experience though.

Sunday, October 25, 2015

I've been using DATS to test a few drivers and inductors I have lying around. I also tried measuring the Focal Profile 918s and made a startling discovery. The minimum impedance is around 2.3 Ohms! Also, the impedance between 75 and 250Hz remains below 3 Ohms.

No wonder these speakers can tell the difference between a mediocre and stout amplifier. They are just ridiculously difficult to drive for their class.

This low impedance is probably a direct result of the crossover topology, 2.5 way means that the mid/woofer and woofer are both working in the bass. Since both are about 6 Ohm devices this would imply a minimum impedance of half this. Ouch.

Please note the maximum and rising impedance in the treble are probably my fault. I've made some EQ changes to the treble which means this is probably not what a stock speaker would measure like above 1 kHz.

Sunday, October 18, 2015

I was so excited to get one of these in the mail I wanted to start blogging right away. I'll cover the response and harmonic distortion measurements in a future posting.

Electrical

Based on my handy dandy DATS V2:

Fs = 1666
Re=6.105
Le=9.47 uH

As expected with such low inductance, the phase plot is practically flat. Highest measured impedance was around 6.4 ohms at resonance. Compared to dynamic drivers, this is a remarkably simple and resistive load.

Mechanics

The mechanical drawing, while accurate, doesn't really do the size of the body justice. The body is really big about the size of some laptop chargers and the flange top/bottom are small and difficult to cut for.

The front of the tweeter. Sorry about the rotation. Note blemishes are due to the plastic shipping film still being on. Kind of a boring shot.

Here is a side view of the tweeter where we can see just how monstruous the body really is. Mundorf provides a rubberized pad on the flange.

Here are a couple of interesting things. Unlike my expectations, Mundorf provides full sized banana jacks and a pair of banana spring clips to attach speaker wire to. I was expecting spade lugs or quick disconnects. The left edge is the bottom of the tweeter. Notice the big difference in the width of the flange on the sides (top) vs. the top and bottom (left). As Lee Taylor of Taylor Speakers pointed out, this can be a real bothersome situation for a cabinet maker. I suspect the choice was to make this tweeter more palatable for line-array speakers. In fact I'm kind of tempted to start working on one next.

Also, the corner radius are very small and non-standard 4mm. Just to be nice, I'll throw in the dimensions below. As you can see there, there is a 5mm spacing on the top and bottom flanges. That's not a mistake. One last comment, the housing is rater flimsy. It feels like a thin version of the poly carbonate material in the uber-expensive suitcases being sold today and there is no visible way to remove it. Speaker makers using this would probably want to encase the driver in it's own, well damped, sub cabinet.

For me this is a bit like Christmas and my Birthday present. Madisound was kind enough to drop ship one set of tweeter and woofers over to Lee Taylor over at Taylor Speakers. While he is busy with the speaker cabinets I can at least play with them and do some basic tests. That's all fine and dandy, but something else happened I did not expect. You can see the problem here.

I did not realize that the speakers were packed in pairs. Madisound did a fine job of packing and shiping, but if I had known this was the consequence I might have bought all the drivers at once. Here's the same view of the tweeter box.

I have gone far beyond merely upgrading with this project so I wanted to start a new blog for everything I work on and discover along the way.

In "Random Acts of Upgrades" I discussed modifying my Focal Profile 918's. So far I've had quite a bit of success but I decided to take the plunge and purchase real tools, as well as stop spending so much money on a pair of old speakers.

So far for this blog I have lots to talk about. The Dayton Audio Ominmic and DATS V2 combination, the Focal's and how they measure, as well as a completely new speaker design I'm calling "No Es Nada" for now. There's a famous kit offered by Madisound called NADA which got me on my way to my very custom speaker design. In Spanish "Nada" means "Nothing." So, this design is not Nada and not nothing, so "No Es Nada" (NeN for short) means "Not Nothing."

First, for my skill level and experience I am spending way too much money. I'm sorry. I know this. I wanted something compact and great sounding, but wanted to go my own way. I disliked the idea of building a kit everyone else built. Also, I didn't like the ragedness in the SS Beryllium's response. So I went looking for alternatives and ended up at the NeN design, which uses a Mundorf AMT and SS Revelator.

So this blog will absorb my further Focal tweaks as well as the NeN build, and Dayton tools review.

I hope others come join me on my journey.

If this fails, I'm going to work on home brewed cruise missiles. Maybe I'll offer cruise missile targeting as a web service. You only get 60% accuracy per missile, but at a great discount. Hah. That's a joke, but I wouldn't be surprised if someone offers that within my lifetime. Some one call me when it happens.